The present invention relates generally to ink jet printers, and more particularly, to such a printer having a dual function air cooling and drying system.
Ink jet printers include several types including the so-called “drop-on-demand” type that has at least one printhead from which droplets of ink are directed towards a recording medium. Within the printhead, the ink may be contained in a plurality of channels and energy pulses are used to cause the droplets of ink to be expelled, as required, from orifices at the ends of the channels.
In a thermal ink jet printer, the energy pulses are usually produced by resistors, each located in a respective one of the channels, which are individually addressable by current pulses to heat and vaporize ink in the channels. As a vapor bubble grows in any one of the channels, ink bulges from the channel orifice or nozzle until the current pulse has ceased and the bubble begins to collapse. At that stage, the ink within the channel retracts and separates from the bulging ink which forms a droplet moving in a direction away from the channel and towards a recording medium. The channel is then refilled by capillary action, drawing ink from a supply container.
One particular example of a type of thermal ink jet printer is described in U.S. Pat. No. 4,638,337. That printer is of the carriage type and has a plurality of printheads, each with its own ink supply cartridge, mounted on a reciprocating carriage. The channel orifices or nozzles in each printhead are aligned perpendicular to the line of movement of the carriage and a swath of information is printed on the stationary recording medium as the carriage is moved in one direction. The recording medium is then stepped, perpendicular to the line of carriage movement, by a distance equal to the width of the printed swath and the carriage is then moved in the reverse direction to print another swath of information.
Typically, such ink jet printers have electronic components that include a power supply, integrated circuit components, controller chips and the like, most of which become hot from use and may require cooling. Generally, heatsinks and cooling devices are used for such cooling in order to keep the printer printing effectively for long periods.
The amount of information that is printed on sheets, and hence the actual quantity of liquid ink deposited on sheets, varies greatly from sheet to sheet. In addition, there is a general and customer desired trend to have ink jet printers that are capable of printing a greater and greater number of pages or sheets per minute.
Unfortunately, as is well known, liquid ink images printed as such ordinarily include excess moisture (generally water) on the surface of printed sheets that must be removed within a set time period and before the sheets are stacked. If the sheets are stacked before the liquid ink images are dry, image smearing and image offset defects typically occur. Devices that actively remove moisture, specifically water, from the sheet surface are referred to as dryers.
Conventionally, separate or stand alone dryers that are constantly on, and that blow a constant volume of hot air, are used for drying such liquid ink images. Dryers of this type that are used in this manner, are ordinarily costly, would tend to be bulky for faster and faster (pages per minute) printers, and could actually damage a liquid image if the volume or velocity of air being blown is too much or too soon for a particular liquid ink image.